In accessing the tops of rolling stock (tank trucks, tank railroad cars, etc.), a gangway or bridge is used to allow workers to move cargo from an elevated loading platform to the top of the rolling stock. These gangways include cantilevers that usually carry a protective enclosure (aka cage) added to the outboard end to provide fall protection while the worker is on top of the rolling stock. In one type of these gangways such as disclosed in U.S. Pat. Nos. 5,042,612; 5,392,878 and 7,140,467, one end of each of the respective cantilevers can be carried on a respective stanchion that extends vertically from one respective end of the loading platform. The cantilever rides up and down along the stanchion like an elevator car between a relatively elevated stowed orientation with respect to the top of rolling stock and a relatively lowered operative orientation with respect to the top of rolling stock.
In another type of these gangways such as disclosed in U.S. Pat. Nos. 4,679,657; 7,216,741 and 8,015,647, one end of each of the respective cantilevers is pivotally connected to one respective end of the loading platform and can be moved pivotally like a drawbridge between a relatively elevated stowed orientation respect to the top of rolling stock and a relatively lowered operative orientation with respect to the top of rolling stock.
However, when the gangway is raised to the stored position, it is important that the bottom of the enclosure has clearance above the rolling stock so that the enclosure avoids contact with the rolling stock and the equipment used to move the rolling stock. In the case of railroads for example, there can be clearance envelopes that must be maintained.
There are many instances in which the clearance height at the outboard side of the enclosure can become inadequate to avoid coming into contact with the rolling stock or the equipment used to move the rolling stock. Such instances can arise when the outboard side of the enclosure leans or that deflects due to the size and/or weight of the enclosure. Such instances can arise from a loading rack that isn't level or from fabrication tolerances.
In the past, this leaning of the outboard side of the enclosure was compensated by anticipating the deflection and designing for it or by the use of shims. However, because both the size and the weight of the enclosures has increased greatly to provide an increased level of fall protection, designs that compensate for the anticipated leaning of these much larger and heavier enclosures are very costly and/or otherwise impractical.
The accompanying drawings, which are incorporated in and constitute a part of this specification, illustrate at least one presently preferred embodiment of the invention as well as some alternative embodiments. These drawings, together with the written description, serve to explain the principles of the invention but by no means are intended to be exhaustive of all of the possible manifestations of the invention.